The present invention relates to a plasma cutting device, and in particular to the one in which work gas is made revolving around the plasma arc.
Currently, a plasma cutting device has an electrode with a flat head in which hafnium, zirconium and the like is embedded. As shown in FIG. 2, such a plasma cutting device is further provided with a supply port 8 formed through a guide can 9 for making work gas 1 revolve. The guide can 9 insulates an electrode 5 from a nozzle 10 having an exhaust port 17. A swirl flow 7 of work gas 1 supplied from the supply port 8 into a swirl flow space 11 keeps plasma arc 13 in the vicinity of a center line 20 of the electrode 5. The swirl flow 7 is then jetted as jet gas 16 from the exhaust port 17 toward a work 14 to be cut.
In the related art plasma cutting device, activated gas, such as air, oxygen or the like has been increasingly used in order to cut the soft steel. This is because such activated gas will accelerate the cut speed owing to the heated work through oxidation and eliminate melt produced at the cut part by oxidizing the melt. In the above case, the flow rate of the work gas jetted from the exhaust port of the nozzle should not exceed the amount required for oxidizing the melt of the work to remove the resulted oxide away. It is widely known that otherwise the surface roughness of the cut surface will be deteriorated.
In the aforementioned conventional plasma cutting device, the flow rate of the jet gas jetted from the nozzle is equivalent to that of the swirl gas. In order to keep the plasma arc around the center line of the electrode for improving the cut surface, both flow rate and velocity of the swirl gas are required to be increased. However, this will also increase the flow rate of the jet gas more than necessary, resulting in deteriorating the cut surface.